1. Field of the Invention
The present invention relates to a pneumatic radial tire, and more particularly the invention relates to an improvement on the contour profile of a tread portion in an asymmetric radial tire.
2. Related Art Statement
It is well known that uneven wear is frequently produced at one side edge portion of a tread than at the other side edge portion under various conditions such as vehicle wheel alignment, transverse gradient of roads, tread base present in vehicle right and left wheels, etc. For instance, when the wheel alignment is set at toe-in, the outer side of the tread is more likely to be worn, while when the wheel alignment is set at toe-out, the inner side of the tread is more likely to be worn. In the case that a road has a gradient transversely inclined towards its shoulder portion, the tread edge portion on the side of the road shoulder portion is likely to be locally worn out. It has been recognized that uneven wear at the tread side portion of the tread may be effectively restrained by increasing the gound contact pressure of the edge portion of the tread on the side which is more likely to be locally worn and restraining slip at this tread edge.
In contrast to ordinary tires having a symmetrical tread contour profile with respect to the tire maximum outer diameter portion, that is, the equatorial plane, there have been proposed and actually used tires having an asymmetrical tread contour profile on the basis of the above recognition. Such conventional asymmetrical tires are so constituted that the equatorial plane is made coincident with the central plane of a wheel, and the radius of curvature of the tread portion is varied between the opposite sides of the equatorial plane, while the centers of the curvatures are positioned in the wheel central plane.